vga_set_atr
vga_set_atr(VGA_REG_BASE, VGA_AC_MODE_CONTROL, atr);
void vga_set_atr(int, int, int);
vga_set_atr(VGA_REG_BASE, VGA_AC_MODE_CONTROL, val);
vga_set_atr(VGA_REG_BASE, VGA_AC_MODE_CONTROL, reg[6]);